I've spent a year on MBTI forums and 6 months on socionics forums (
http://www.the16types.info/vbulletin/index.php) and from what I can tell, yes, they are the same system. Both systems use the same N-S and T-F dichotomies that describe exactly same underlying phenomena in human psyche, just that they use different wording to describe it.
I like socionics forums more than MBTI forums for their heavier focus on theoretical discussion, but the system itself is nothing new really. Using my knowledge of MBTI I got into Socionics quite easily.
Best type correlations are as follows:
ENFP (IEE) INFP (EII) - delta
INFJ (IEI) ENFJ (EIE) - beta
ENTP (ILE) INTP (LII) - alpha
INTJ (ILI) ENTJ (LIE) - gamma
ESTP (SLE) ISTP (LSI) - beta
ISTJ (SLI) ESTJ (LSE) - delta
ESFP (SEE) ISFP (ESI) - gamma
ISFJ (SEI) ESFJ (ESE) - alpha
Alpha, Beta, Gamma, and Delta are quadra, groupings of 4 types that value the same functions.
Alpha values Ne, Ti, Fe, Si
Beta values Ni, Ti, Fe, Se
Gamma values Ni, Te, Fi, Se
Delta values Ne, Fi, Te, Si